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What kind of cameras are onboard high altitude UAVs that aid in its control?
I ask this question in the context of people flying their drones much higher than the usual hobby planes. Satellite based GPS navigated Autopilots using photogrammetry and/ or military drones.
What kind of cameras do first-person-view (FPV) pilots use and mount onboard to control the plane, and not for any sensors to collect data/ perform other tasks?

The Bottom Line Up Front
Infrared and visual video cameras aid in navigation of larger class UAVs and are helpful for safety but do not satisfy the legal requirements for unmanned aircraft to operate in US/international airspace. Instead, the use of onboard navigation systems like GPS, combined with air traffic control services and common flight safety rules allow safe navigation of high and medium altitude UAVs.
What UAVs Operate at High Altitude?
Northrop Grumman's "RQ-4" variants (e.g. USAF RQ-4B Global Hawk, US Navy MQ-4C Triton, NATO RQ-4D Phoenix) are the only widely recognized UAVs flown at high altitudes (FL500-600). The RQ-4 is also the largest UAV with a wingspan greater than a Boeing 757.  All other UAVs, including the MQ-9 Reaper, operate at medium or low altitudes.

How Does the RQ-4 Navigate?
The RQ-4 has sophisticated, GPS & gyro-enabled navigation computers that ensure it always knows where it is and where it is going. To avoid airborne hazards like other aircraft or bad weather, it follows the same instrument flight 'rules of the road' that manned aircraft rely on when flying at night or in the clouds. Specifically, air traffic controllers use radar to track aircraft from the ground and alert the pilots if they see an unsafe situation on their radar screens. These instances are rare, however, because everyone follows their flight plan and obeys air traffic controllers' instructions in order to remain safely separated in the air--even remotely piloted aircraft.
Does the RQ-4 Have Any Cameras Used to Aid in its Control?
Yes. As a backup to air traffic control clearances to taxi, takeoff, and land, the RQ-4 has a forward-facing infrared video camera on the nose of the airplane.  Although it is not legally required to have this camera, it is used only as a backup for the pilot to ensure the runway is clear of obstacles during taxi and prior to landing on the runway. Radio transmission of the video camera signal is via line-of-sight antennas only (not over satellites), so therefore it is limited only to the airfield/runway environment where the ground control station is located and is not used while away from the airfield during climb, cruise, or descent.

Note there are two small windows in the pressurized camera compartment: One upper window for the video camera lens and the lower window used to display the pressure dial for the camera compartment.
What About Medium/Low Altitude UAVs?
Medium altitude UAVs like the MQ-9 predator carry a variety of infrared (day/night) and electro-optical (day only) full motion video cameras used primarily for their mission rather than for navigation. Unlike the high-altitude RQ-4, they operate at the same altitude levels as commercial air traffic.  They can follow the same instrument flight 'rules of the road' that manned aircraft do when flying at night or in the clouds. Often, their mission requires them to fly in areas where following these rules aren't required by all aircraft. In this type of airspace, pilots of smaller aircraft like gliders and crop-dusters don't have the radios to communicate to air traffic control and count on other aircraft to 'see-and-avoid' them instead. The MQ-9 does not have a pilot onboard to look out the window and avoid these 'visual flight only' aircraft, so it needs other solutions to ensure safe navigation.
The MQ-9 does have a powerful ball-mounted, full-motion video camera onboard. However, the USA's Federal Aviation Administration and the worldwide International Civil Aviation Organization has not deemed the use of this camera as a sufficient substitute for the see-and-avoid requirement. Therefore, despite the MQ-9's robust visual/infrared camera system, it must rely on other methods of deconfliction like temporary/military restricted airspace, special clearances, and even chase airplanes, in order to conduct its training in the US and its missions overseas.  The same challenges exist with smaller, low-altitude military unmanned aerial systems and commercially operated drones.

Are Cameras Any Good For Long Range Navigation?
That depends on what you consider long range. Navigation using cameras, especially to avoid other aircraft, requires low-latency. It does little good to see a rogue aircraft filling your windscreen if, by the time you see it on the screen, the plane has already crashed into your UAV. This usually isn't a problem for FPV hobbyists because they have a line of sight video signal, directly from the RC aircraft, that feels instantaneous to the pilot wearing FPV goggles. On the other hand, truly long ranges require operation beyond line of sight, relying on satellites to pass information to/from the aircraft. This extra architecture causes video latency, sometimes up to multiple seconds, making it nearly impossible to visually react to a time-critical safety event.

A Better Alternative to Cameras
In addition to the video latency problem, video cameras on medium/high altitude UAVs are specialized to focus on small targets at long range--not scanning the skies for unidentified aircraft. Imagine trying to spot a fly buzzing around you while looking through a toilet paper tube. An additional, wide-angle navigation camera/lens could be carried on the aircraft but it would not be worth the additional cost, weight, space, and power consumption. Instead, long-range aircraft like the RQ-4 and MQ-9 rely on a framework of aircraft regulations, ground-based air traffic control, and segregated airspace to safely navigate.
Note: This response was drafted from scratch, solely to answer Rajath's question about cameras on high altitude UAVs. Thanks in advance for your feedback.

Welcome to Aviation.SE! Awesome first answer!

I'll mention two of my favorites.
MQ-9 Reaper

The Reaper has the "Multi Spectral Targeting System", which is an array of visual cameras and sensors - this includes an infrared sensor, color/monochrome daylight TV camera, and an image-intensified TV camera, each of which can be used independently or combined to provide one video stream. Specific details are classified, but the ARGUS system has been equipped to some drones, and that system itself displays 1.8 billion pixels - that's made up of 350+ 5 Megapixel cameras.
RQ-4 Global Hawk

The Globalhawk is not so much a weapons platform, as it is a sensor, targeting, and surveillance platform. Details are again classified, but it is known to have an incredibly powerful camera of resolution comparable to the ARGUS pod system. It is even being tested with the camera system from the U-2 spyplane.
"First Person" or "Cockpit Camera"
Regarding the cameras actually used for flying (not surveillance), both aircraft come equipped with a built-in front facing color camera. This is a much lower resolution, but still of high quality, and is primarily used for landing, takeoff, ground operations, and low flight. There is not much need for this camera view when in the air, as you'll either see white or blue! In the below image of a MQ-9 Reaper control station, you can see the pilots having the front-facing screen pulled up. It's important to note that similar to a hobbyist, they also have task based GPS navigation. The pilots flip it to autopilot once they're airborne, and typically manually control it when you're at your area of operations.

I'll also mention that I quite honestly chose that particular picture of the Global Hawk because the guy looks like he's having a blast on the tug!

The Predator drone has an array of optics for various regimes of flight (there is no citation on wiki for this so take it at face value):

The aircraft is equipped with the AN/AAS-52 Multi-spectral Targeting
  System, a color nose camera (generally used by the pilot for flight
  control), a variable aperture day-TV camera, and a variable aperture
  thermographic camera (for low light/night). Previously, Predators were
  equipped with a synthetic aperture radar for looking through smoke,
  clouds or haze, but lack of use validated its removal to reduce weight
  and conserve fuel. The cameras produce full motion video and the
  synthetic aperture radar produced still frame radar images.

The Predator also has a Raytheon built Multi-Spectral Targeting System (MTS).


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How can a pilot deal with a magneto failure?
As I know, the engine is independent from the electrical system, and it is supplied from magnetos. However, how can a pilot deal with a magneto failure? And also, when one magneto fails what problems can occur?

One of the things the checklist will have you do prior to lining up on the runway in a piston engine aircraft is a magneto check. That serves to verify that both magnetos are in good working order and that the grounding of both magnetos is intact.
Typically, that will involve bringing the engine to some given power setting (most likely expressed in terms of RPM, but I suppose it could be measured in some other way for some engines; manifold pressure, maybe?) while holding position, then turn one magneto off, then back on, then turn the other off, then back on. While doing so, you verify that there is a drop in engine power, and that the drop in power is symmetric (about the same for both magnetos), and of course that the engine keeps running on either magneto alone.
This verifies that both ignition systems (magneto, spark plug, etc.) are working, and that the grounding of the magnetos works as expected. Absent the power drop, you could have a hot magneto, which isn't a huge problem in flight but could be a major headache on the ground.
If a magneto fails in flight, especially in a single you might not even notice initially; there will be a slight reduction of engine power, just like during the magneto check, but the engine will keep humming along on the remaining magneto. That's part of the purpose of having two independent ignition systems: redundancy.
If there is an engine failure in flight, the checklist will likely dictate something like "select best magneto" at one point or another during the restart sequence. Basically, you'd be doing a magneto check in the air, and choosing whichever setting gives you more power. If one magneto has failed outright, this will very likely cause the engine to stop when you select only the bad magneto; you'd then have to select the other (or both) and restart the engine again.
The checklist may or may not specify that you should land as soon as possible after a magneto failure, but if it were me, I'd want to land regardless and have the problem checked out properly. That would mean either just landing and taxiing back to the ramp (if, say, you're in the pattern doing circuits), or diverting and landing (if you're on your way to somewhere). There's always the possibility that whatever caused the first magneto to fail might cause the second to fail as well, and I'd rather be on the ground at the wrong airport than in the air with a non-functional engine.

Generally when you have a mag malfunction you want it turned off.  The mag may just quit entirely, but there are other failure modes, such as loss of spark to one or more plugs, or worse, a shift in the mag's internal timing, and either of those can cause rough running and potentially detonation (where something causes the timing to drift in the advance direction - the mag's timing is fixed and is set mainly by its orientation on its mounting pad on the engine, but there is an internal timing process for the breaker points when the mag is set up on the bench, called setting the P-gap).
Because of this, one of the normal things to do with a rough running engine is to switch to each mag and see if the roughness stops.
The main effect of having a mag switched off is the obvious one, a loss of redundancy, and a small power reduction.  Aircraft cylinders being quite large, the flame has a long way to go to the other side of the combustion chamber when the plug fires.  Dual plugs ignites the mixture on opposite sides of the cylinder at the same time, and the flame just has to travel from each side to meet in the middle.  One a single plug, the flame travels from the single ignition point across to the other side and this takes twice as long.  The effect is more or less similar to retarding the timing a bit; delayed build-up of combustion pressure and less complete combustion, so there is a reduction in horsepower of a few percent.
Also note that if a mag completely stops working while you're in cruise, without any intermediate roughness, you probably won't notice it (unless you were intently starting at the tach or carefully focused in on the sound) and will be unaware of it until the next runup on the ground.  You might notice the change if it happens at take off power, on a fixed pitch propeller, from the RPM drop, but if it's a constant speed prop, you won't detect the change as an RPM change and you may or may not notice the subtle change in sound as engine torque declines slightly.
A dormant failure of a single mag that lasts for one flight is an insignificant risk, so it's not like you need to continuously check the mags any more often than once per flight (and even that's overkill; when I was bush flying we only did a full run-up first flight of the day, although on subsequent flights I would usually quickly flip between the two while taxing to the end of the lake for takeoff, just to confirm they were both working).

If one magneto circuit fails, the engine keeps running, if only with one spark per cylinder, and there may be a very slight reduction of power. The only real risk is that the other circuit may fail too, and in that case the power will drop to zero...

So how can I troubleshoot this problem? is there any solution?

Turn off one mag - if there's no drop in RPM then you've turned off a dead magneto and the other one is still good; if the engine stops then you've turned off the good magneto, and the other one is dead; if there's a slight drop in RPM then both magnetos are good.

Troubleshoot, not much you can do airborne. If you had been flying at a high altitude, descending might help if the points had been arcing out. Not much else you can in the air.  On the ground you can check to see if there are any wiring problems or mag to plug wiring problems, check for cracks in the case, open the mag & check the points, check the capacitor if it has one, mags for small Cessnas have a nylon gear that ages & breaks, check the shaft to see that it's still being solidly driven, etc.  Mags in my plane get sent to a shop in Rockville, IL for IRAN every 500 hours or less.

In the air you don't have a lot of information about the core problem. the only controls you have are :turning off/on magnetos, Carb heat, fuel pump, and/or mixture (or occasionally checking fuses). nothing else while in the air.

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Could the cargo hold of an aircraft be re-designed to carry passengers?
This image had me intrigued:

It looks like two semi-circles, the upper part for passengers and the lower part for cargo.
I was wondering, for short haul flights, could the lower part be converted like the upper part, so the plane could carry more passengers, like a basement stuff, no windows and lower fares. We could do away with cabin luggage and stuff to take care of maximum takeoff weight, and anyways my thought was towards short haul flights.

A.K.A. a refugee plane.

they could just sit on the floor, like Operation Solomon which flew 1,122 pax on a 747 from Ethiopia to Israel  http://israelforever.org/news/operation_solomon/

Or like operation babylift, but that didn't turn out so well.

In principle, yes. The cargo hold is pressurised and (depending on the aircraft and the installed options) reasonably temperature-controlled. However, it's probably not feasible; there are three major issues to be worked out that I can think of off the top of my head:

Cargo hold height and windows. It's a bit hard to tell from your picture, but even on a large widebody plane the cargohold is not that high (the cabin floor is lower than halfway). The A330 (as an example) carries LD3 containers in its cargohold, which are about 160cm tall; the cargohold is not much taller than that. Most passengers cannot walk upright inside it; the cargo hold on smaller aircraft is even lower (the one on the A320 is designed to carry LD3-46 containers, which have a height of about 115cm). Also, the lack of windows would bother passengers in the lower deck.
Emergency exits. In an emergency, passengers must be able to get out of the plane within 90 seconds. At best you would need to install additional doors in the cargo hold; at worst, you will not be able to meet this requirement (because of the low ceiling, people can't move as quickly)
In a crash landing, the lower fuselage may buckle, which serves to cushion the impact for the people in the passenger cabin. You would need to show that the passengers in the lower deck can survive a crash landing.

Note that some airlines use part of their lower deck for galleys, crew rests and even lavatories.

I would add that: You need a lot of the space anyway, for passenger luggage. Only part of the cargo hold is used for 3rd party cargo. You can argue that lowcost airlines need less, but do they need that much less?

Lower fuselage lobe has been used for passengers in the past. A330 is certified for such and in Japan the 747 - 100 was also used regularly for very short flights with pax in the lower lobe.

Sources for this?

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Is it ok to lift locked armrests on aisle or window seats?
While reading this question, I came across a little trick, of how to lift up the locked arm-rests in window and aisle seats. Though I always wondered why they were locked, knowing that little trick now makes me wonder is it legal to lift locked arm-rests. Would it get me into any trouble with the cabin crews or the airline?

@egid A passenger could knowingly move the armrest out of its locked position just before takeoff—while the cabin crew were watching, thus necessitating their intervention—but, based on any information we currently have in this or the linked supposed duplicate question/answer, that passenger has not performed any illegal action.

@Firee This doesn't answer your question, but I have frequently moved the isle armrest to the full upright position both during flight and after shutdown; as I recall, my actions have never received any notice of the cabin crew.

PLEASE NOTE: There is a Meta discussion about the suitability of this question.  Please refer to that discussion for the Meta issues surrounding this question rather than comment here.

I'll have a go at this, but this answer applies only to the US.
First, is it legal? As far as I can see, yes. There are various regulations (e.g. 14 CFR 121.317) about specific items that passengers have to be briefed on and comply with instructions on. They include smoking, seatbelts, emergency exits, screens and tables etc. But there's no explicit mention of armrests and I didn't see any generic clause like "any other equipment" or whatever. So in the absence of any explicit or general regulation that says you can't, I would say you can.
Second, will it get you "into trouble"? Maybe. As the answer to a related question shows, the FAA doesn't want armrests to become an obstacle to evacuation and they advise crew members to make sure that armrests are locked down for takeoff and landing. Many airlines I've traveled on have an announcement about the armrests, even if there's no regulation that requires it. If the crew ask you to put your armrest down and you refuse then the 'best' thing that can happen is that they decide you're rude but not dangerous and let it go. But if you refuse repeatedly and they decide you're being confrontational or unlikely to follow other instructions then 14 CFR 91.11 would apply:

No person may assault, threaten, intimidate, or interfere with a
  crewmember in the performance of the crewmember's duties aboard an
  aircraft being operated.

Under that regulation, if the crew decides you're "interfering" with their duties (which include keeping you and everyone else safe), you'll probably get a police escort off the aircraft, especially if alcohol is involved.
But having said all that, I don't think this is a big deal at all. The FAA's concern seems to be about armrests that get stuck at an angle, not about ones that can be fully lifted. I've often seen passengers put up their armrests and I've never heard a crew member comment on it, but if they do ask you to lower them, arguing about regulations would probably be a bad idea.

But having said all that, I don't think this is a big deal at all. : I think that summarizes it properly. Personally I never heard announcements to put the armrests back in position, though I never saw anybody move it in the first place. So many times I wanted to move it, in order to get up and give way to my co-passengers who wanted to use the loo. Am itching to try it the next time I fly on April 4th.

At least in the UK, it is illegal not to comply with a lawful instruction given by a cabin crew member. "Lawful instruction" means one which itself is not illegal, nor would cause you to do something illegal. Thus, even though armrests might not be specifically mentioned, if a crew member instructs you to raise or lower it, that instruction is lawful and you commit an offence if you do not comply. Regarding the OP, I've never heard any instructions to do anything with armrests other than for take-off and landing so, if you raise it, and lower it when instructed, you are doing nothing wrong.

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Can an armed door be opened from outside an airliner?
This is a continuation from this question, whereby it discussed the meaning and significance of an armed door.
Now, is it possible to open an armed door from outside, for example, if for some reason the passenger or crew are incapacitated, due to inhalation of poisonous gasses etc.

This depends on the aircraft:
DC9, MD80, B727, B737
On some (especially older model) aircraft doors such as the Boeing 737 for instance this is directly dangerous, since the slide is attached on the inside by hand with the means of a girt bar to the aircraft.
There is hence no way to open the door without the slide going off should it be armed. There is a helpful notice in red on the outside to "stand clear" when the red banner is crosses the window, the indication that it is armed. Judging by the space required and force the doors have, this is still most probably very dangerous idea that should not be used unless absolutely necessary.

Source
Airbus, B757, B767, B777, MD11, E-Jets
On more modern aircraft, this is safe: opening the door externally will push the arm handle to the disarmed position before proceeding to open it. This is for instance the case on all Airbus aircraft.

This video provides a nice example.

Nice explanation there and the video.. Does the Airbus have any mechanism to prevent opening of doors from outside, thinking from safety POV...

@Firee safety in what sense or scenario? Not that I know of...

@Firee. from a safety POV it is desirable that the door can be opened from outside. From a security POV there is the airport security staff.


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If a commercial airliner enters into a spin at high altitude, is it possible to recover?
Often flying I have this fear, that something will snap, and the plane will start plunging to the ground in a spin.
My question is, once a passenger aircraft (e.g. an A320) goes into a spin, can the pilots recover it, stabilize it and make it glide, or is it too late?
A similar question was asked before, but I am looking specifically for answers regarding large passenger aircraft.

Hello Firee, welcome to Aviation.SE. Questions about hypothetical situations like this are impossible to answer. 'some technical snag' is not really defined, so we can't analyse how that would affect spin recovery possibilities. In general though, spins are recoverable especially from high altitudes. See for example this question

To reassure you, large airliners enter into spins veeeeeeery rarely

As DeltaLima said, it is kind of hard answering your question.
After looking at the question he linked you might have found the answer already.
Let me try to answer your specific question though:
Assuming an airliner, let's say the A320, for some reason got into a spin, can it be recovered? The general answer would be yes!
Here are some things to consider though:
The FAA requires all single-engine normal category aircraft to demonstrate spin recovery in FAR 23.221(2).
It depends a lot on the center of gravity of the airplane whether it is recoverable from a  spin or not. If the center of gravity is too far aft, it will not be recoverable from a spin. Gliders, being light, have an easy shiftable CG, and there is some that don't enter spins at all or need extra weights in the back in order to make them spinnable! Airliners are not required to do so as they are not as likely to get into a spin in the first place!
The structure of an airliner is designed for air flowing over it, not for being in a spin! Centrifugal forces will be applied to the structure due to angular acceleration. Also, spins by airliner would be a lot faster then by little aircraft and more forces would be applied to the frame. If the recovery from the spin is made too fast or abrupt, it can overstress the airplane as well!
All Airbus I know are fly-by-wire, and Airbus is well known for its computer based controls. Most airliners have a lot of systems, which prevent them from even getting into a stall. There a incidents where these systems failed and it went back to the pilot doing the right thing.
As a spin always always always requires a stall first, and pilots are trained to avoid stalls in the first place, it is very unlikely for an airliner to enter a spin, having the pilot and various systems working against entering a stall!

Dear Maverick, Thanks is the least I can covey, for making this effort to answer my question and provide me some relief. It's a much better answer I feel than what was linked.

I have read it was pilot error, with Cpt. Asseline allowing the aircraft to get too low and slow to recover safely.  Do you have a reference for the claim of conflicting aircraft systems?

I'm afraid that is something that I was told by somebody who was there, but I will see if I can find something!

Reading the Wikipedia article about Air France Flight 296 it (and I tend to trust those quite a bit) doesn't say what really went wrong. And there is the conspiracy theory that Airbus has switched some equipment to cover up, it might be a problem in the fly-by-wire system, and I think that's what they say on the corresponding "Mayday" episode. If there are any solid facts that anybody can find, please let us know!

@Maverick283 : I have watched the video linked by you, and I must say it was spine chilling experience. Thanks for sharing it because I did not know of this. Thinking about it now, is it true that there were passengers also in it?

@Maverick283: It's well known what went wrong in AF296. The crew took it too low and too slow and the engines were not able to spool up fast enough to allow the aircraft to climb out. The alpha-limit electronics worked as intended, otherwise they would have likely stalled (they didn't) and hit the ground much harder. The alpha-protection was disabled (intentionally) so it could not spool up the engines earlier and get them out. There is no confusion about this in the Wikipedia page or in the investigation report. Other theories (like in the document) are not really credible.

@Firee: Yes, there were passengers. The people in AF who came up with this stunt grossly underestimated the risk and put people in. Most of them survived, many even without serious injuries, but there were 3 fatalities.

(-1, the narrative about AF296 is wrong, nonsensical and evil)

Alright, thanks for sharing this, I'll redo my question to fit that, I just didn't know this and thought it'd be a good example as to my knowledge it happened that way.

"if forces get too strong, an airliner is much more likely to break apart in a spin" -- spins are 1G maneuvers. If you manage to get out of the spin, its the pull out from the dive that will break the airplane apart. if you pull out too hard, you will pull a lot of Gs and possibly enter a secondary stall. if you pull out too slowly, you will exceed Vne.

Correct, a wrong or to rapid recovery from a spin will most likely overstress the airframe. Loads during a spin itself are complex, poorly understood, but generally unlikely to damage the airframe. As a spin is a rotating motion, angular acceleration will cause G-forces in vertical directions, unusual to those normally occurring during flight. I'll edit the question to make it more  accurate on this topic.

How to stabilize a spinning aircraft
Stabilizing a spinning aircraft is fairly easy. If the center of gravity is not too far forward, the rudder is deflected in spin direction and the elevator fully up (adjusting the horizontal tail trim helps, too), the spin will continue until the aircraft hits the ground. In some cases, the spin might oscillate between two stable modes, and the aircraft will continuously pitch up and down between them. An airliner with its high wing loading will loose a couple of hundred meters per turn in a spin, but will not accelerate once the spin has fully developed. Increasing air density on the way down will actually decrease the rate of descent.
But I guess you wanted to ask something entirely different.
Ending a spin
Ending the spin is equally easy and is performed by the opposite commands which stabilize the spin. Proving that the aircraft will easily come out of a spin is actually part of certification requirements. The stable rate of descent gives the pilots ample time to end the spin, and even if the engines have failed, emergency systems will ensure that the pilots can control the aircraft. The risk that an otherwise normal flight will end in an unrecoverable spin is practically zero.
I would actually prefer that the airplane enters a spin. If the center of gravity is in the forward part of the allowed range, it is more likely that it will enter a spiral dive after stalling. Now the pilots need to react quickly and with measure, because drag is much lower in a spiral dive than in a spin, and the resulting higher speed poses a real danger. For that reason the flight control system in the type of aircraft you mentioned, the A-320, will prevent the aircraft from entering a spiral dive in the first place.
What if something snaps?
So far, we have assumed that all systems work. What if something snaps? The surprising answer is: Mostly nothing. A fundamental design principle for aircraft demands that primary structural parts or equipment can snap without the aircraft breaking apart. This is called redundancy: Every primary structure and every flight-critical piece of equipment is duplicated, so if one part breaks, the other, redundant part will continue to carry the loads and the flight can be terminated as planned. Regular inspections make sure that such damage is caught quickly, and the manufacturers continue to improve the existing fleet once a weakness has been spotted.
Even if something snaps, it is extremely unlikely that the aircraft will enter a spin, and even if this happens, it is easy to end. Your fears are unfounded.

Curious question: Have you ever heard of an airliner entering a spin or spiral dive? I have found nothing and I think only single engine normal category aircraft have to be tested to come out of a spin (FAR 23.221).

@Maverick283: See China Airlines 006. It is also mentioned in one of the linked answers.

@PeterKämpf Thanks for the explanation and the link of China Airlines was excellent, that is something what I was looking for.

@Maverick283: The prototype 737 went into an inadvertent spin during flight testing (the pilots recovered it from the spin and landed safely).

I wouldn't worry about something breaking in an airliner. The chance of that actually happening to you are orders of magnitude smaller than something breaking in your car on the way to the airport. Airline disasters make for much more sensational reading than car accidents do, so they tend to be hyped quite a bit more, but a major accident like that is really quite rare. Plus, there is so much that goes into inspecting those aircraft. Breaks do occur, but they are very rare. It's just not worth worrying about.
And I'll go back to my original answer. Pilots are taught the proper ways to deal with a spin, and a spin is a spin is a spin. The specific aircraft aerodynamics differ, but the general procedures are still the same. However, if you're in an airliner that gets to the point of spinning, then it's more about the pilot than it is the aircraft. And if the pilot let the aircraft even approach a spin, he's the wrong guy to be sitting in that seat to begin with.

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Are turbine engine reconditioned after severe FOD damage caused by bird strikes?
I've just been watching a video of a 757 suffering a bird strike on take off. The pilots continue with their take off, declare a MAYDAY, shut the engine down and proceed to land without any issues.
Link to the video: https://www.youtube.com/watch?v=9KhZwsYtNDE
Are these engine reused after an event like this? Are they sent away to Rolls Royce, Pratt & Whitney etc to be repaired? Or are they always deemed a complete write off and replaced with new?
Obviously turbine engines are highly balanced complex pieces of machinery so I can imagine once FOD has damaged this balancing the damage is pretty high.

@ShaanSingh I've added a link to the video.

The damage is assessed and then a determination is made whether or not its economical to repair the engine.  It will truly be taken on a case by case basis.  However, FOD damage to the engine doesn't automatically mean the engine will be scrapped, and I think you'd be surprised with the damage they can suffer and still remain in service after repair.

Repair and replacement of engine components are performed in accordance with the manufacturer's specifications.  Economic evaluations may be used to determine whether the engine can be serviced in the field, in a service depot (third party or engine manufacturer based), re-built, re-manufactured or scrapped.
In cases where a plane I have flown has ingested FOD (birds, stones, etc.) the first step is normally for the company mechanic to utilize a bore scope for a visual inspection.  In the case of the PT6 engine families, I have observed that no damage is normally found and the engine returns to service.  Obviously that is situational.


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Has there ever been a successful 'bail-out' during an airliner test flight?
Has there ever been an instance of a crew having to 'bail out' during a test flight of a commercial style aircraft (I.e Airbus, Boeing etc)?
I know that test flight crews often wear orange suits, parachutes during preliminary flight in case there is an issue.

related: http://aviation.stackexchange.com/questions/7745/how-does-this-test-flight-escape-aparatus-work

The concorde prototype (it's at Duxford in the UK) had an escape door in it, my understanding is that nobody ever would expect to successfully use it. Having seen it myself I would agree it's pretty unlikely.

After seeing the cockpit escape hatch (http://aviation.stackexchange.com/questions/8199/which-external-instruments-are-visible-on-the-a350s-nose-section/8203#8203) in an Airbus picture, I wonder if it has been tested? I would imagine that anything on an aircraft as (potentially) important (life-saving) as an escape hatch would need to be tested beyond simulation.

@CGCampbell They've obviously been tested on the ground to check that a person can get through them wearing whatever the crew will be wearing. But the only way to test them "live" would be to fit one to a plane that's known to work and then get somebody to jump through it. That would be extremely dangerous and wouldn't necessarily tell you much, since it's a different plane with different airflow. My guess is they're not tested "live": they probably just do their best and hope it won't be needed. A sensibly designed, untested escape hatch is way better than none at all.

@CGCampbell: The escape hatch in that picture looks like a standard cockpit emergency exit that is fitted to production aircraft and intended to be used on the ground only e.g. if the cockpit door is jammed after emergency landing. The additional escape hatch on prototypes intended for parachuting is on the bottom side.

Exiting via the top escape hatch is rather dangerous - you might very well hit the tail.

On the Boeing 727 there is the famous DB Cooper incident.  Not aircrew, and survival is unknown, but it's a datapoint. ;)

@JasonR That was a great read.. thanks!

Can such planes be exited via the cargo bay hatches?

In this experiment to observe a deliberate airliner crash
http://en.wikipedia.org/wiki/2012_Boeing_727_crash_experiment
the crew exited in flight down the tail stairs...


text:
What is the division of tasks among the control towers at Chicago O'Hare airport?
I was at KORD this week for the first time in decades. I spotted 4 control towers (two near the terminals, and one at each end—and I am not sure if I got them all). I was not counting the short ones, obviously for gate control.
What is the division of labor?
Is it anything like KDFW?

I was not counting

There are four on the airport diagram. There are 4 physical towers of an ATC variety.

Google map (3D): 1st image (T2/Hilton)  = Old TWR, now used for coordination --- 2nd image (T2/T3)  = Center TWR --- 3rd image (DLH Cargo) = South TWR --- 4th image (AAL) = North TWR.

Some interesting information about airport configuration, control and radio communications, by CARMA.

Very much related: http://aviation.stackexchange.com/questions/2070/how-does-having-multiple-atc-towers-affect-airport-operations

As mins pointed out, the four towers you are asking about:

Old tower, no direct responsibility
Center tower
South tower
North tower

The airport directory (accessible from AirNav) breaks out the different tower and ground frequencies.

TWR N - 9L/27R
TWR C - All others
TWR S - 10R/28L

This makes sense, as the north and south towers shown on the AD are really only close to those applicable runways. The center tower is located where it can handle the rest. The old tower is not labeled.
The ground control is also split between the towers. I couldn't find a good reference for the division of responsibility there, but I would imagine that it would be similar to that of the towers, only controlling the taxiways associated with those runways, which are hard to see from the center tower.


text:
How hot do internal parts of jet engine get?
How hot does a jet engine get? I'm interested in the temperature of the parts, not of the exhaust or combustion. If you took temperature of an engine after a flight across the Pacific Ocean what are temperatures of stationary and movable parts? A car engine block may be 250 degrees Fahrenheit (120°C). I'm thinking of how to modify the basic architecture.

Related: How are temperature differences handled in a jet engine?

This parameter is called Turbine Inlet Temperature (TIT)

Turbine Inlet Temperature (TIT) is the temperature of the combustion
  chamber exhaust gases as they enter the turbine unit. The gas
  temperature is measured by a number of thermocouples mounted in the
  exhaust stream and is presented on a flight deck gauge in either
  degrees Fahrenheit or degrees Celcius.

Essentially it's the temperature going out of the combustion chamber, representing the highest temperature the turbine would face.
Here's a figure showing how we are doing recently. So we are at around 1800K now and may reach 2000K soon.

For the temperature of the actual part under cooling, here is the current status of materials: we are at around the 1350K mark and may approach 1400K soon.

The reason we're talking about "cooled" is because we're routinely exceeding the temperature at which the turbine blades would melt. So, since the question explicitly mentions "parts temperature, not exhaust temperature" this is somewhat of an overestimation.

You should have included the graph preceding the one you used since it gives maximum part temperature capacity.

just a heads up - the first link doesn't point to an actual URL

@crass_sandwich Fixed.

Impressive use of graphs, but I have never seen a TIT or ITT gauge calibrated in Kelvin.  Could you make this more relatable, and use the same UOMs in the question?  Also, what engine do these graphs represent?

@MichaelHall the first graph lists the engines it represents https://en.wikipedia.org/wiki/Power_Jets_W.1
https://en.wikipedia.org/wiki/Rolls-Royce_Conway
https://en.wikipedia.org/wiki/Rolls-Royce_RB211
https://en.wikipedia.org/wiki/Rolls-Royce_Trent_700 modern engines use different materials in different stages so the materials one won't correspond 1:1 to engines.

What is the typical compressor exit (combustion chamber intake) temperature? I mean maximum temperature just before combustion.

Depends on the section of the engine in question.  The 'hot section' of a jet engine gas core, which consists of the isobaric combustor, high pressure turbine and low pressure turbine, by far, operates at the highest temperatures.  On modern, high performance aviation gas turbines, the high pressure turbine inlet temperatures are reaching nearly 3,600° F (2,000° C) during full power operation.  Exhaust Gas temperatures in the jet pipe just aft of the last low pressure turbine stage are in the neighborhood of 1,000° F (550° C).  Air exiting the high pressure compressor section will be around 500° F (260° C).
A little basic thermodynamics will quickly demonstrate that the hotter you can operate the gas at the beginning of its expansion through the turbine section of the engine, the more efficient the engine will be.  This increase in temperature is, of course limited by the material properties of the metals and composites used to manufacture these engine parts.  Jet engine turbine sections are usually manufactured from novel nickel-cobalt and titanium superalloys using novel single crystal casting techniques for maximum structural strength.  In addition, they also make use of compressor bleed air for use as a boundary layer to prevent direct contact between the walls, stator and rotor blades and the high temperature gases.

What is the typical compressor exit (combustion chamber intake) temperature? I mean maximum temperature just before combustion.

That’s generally in the neighborhood of 500°-600° F, Depending on the OAT as well as the compression ratio.

Compressor exit temperature and turbine inlet temperature are the hottest regions, front and back of combustor respectively. However, it is rare that TIT is directly measured. Most times the inter turbine temperature (ITT - ARP station 4.5) and station 5 (EGT - exit of the low pressure turbine, back of the core stream) are measured and mathematical and thermodynamic models back out what the TIT would be. The cockpit displays EGT, not TIT. But referencing the graph above, the trend is real but it’s not actually measured directly. Too hot back there.


text:
How long does it take, in average, to train for a different plane?
During the Russia-Ukraine war, there are considerations about donating F-16 fighter jets to Ukraine, but there would be problems with providing training for that specific plane. Training for another F-something plane would be provided instead, with information on what is different.
It may ultimately resolve differently (this is a quickly changing situation, as of mid-May 2023) but this made me wonder: how realistic is this within the planned 3 months? (from now on my question becomes generic, not related to the war above)
Specifically, how long is training expected to last for a pilot that switches

military planes within a similar "line" (F-14 to F-16 for instance)
military planes across "lines" (F-16 to Rafale for instance)
commercial planes within a constructor (Boeing something to Boeing something else)
commercial planes across companies

I have no idea about piloting so I do not really feel whether what you know from one plane can be reused in another one. If I take the example of cars, I expect the wheels to be at the same place in a Renault Clio and a Mercedes (obvious case), the same for the blinker (less obvious case) but the button to open the fuel door will be anywhere (I need to check that in the manual). How does this relate to planes?
The training (and the time it takes) I have in mind is the one required to fly the plane with a bit more than fingers crossed (= safe but maybe not optimal). To take again the example of cars, that would be the ability to start and drive but possibly not use the entertainment beyond common usages, or use the automatic windscreen wipers mode (but still be able to change the speed manually)

As an aside, dense SAM coverage has reduced aircraft on both sides to a tiny fraction of their normal effectiveness. Looking cool could still be accomplished.

Switching planes is not like switching cars.
There's at least a hundred distinct steps from getting into a cold dark plane to celebrating mission accomplished. Getting it started is the easy part. Then there's programming and calibrating the systems, programming the munitions, understanding all of the screens and operations they require.
Even switching between USAF and USN aircraft involves a lot of re-learning. Other nations have even more differences in their control philosophy.
The only transferable skills are combat tactics and the basics of aviating. The part of the training after advanced flight training on LIFT (lead-in fighter trainer aircraft) would start over again.
The minimum time to switch airframes is generally half a year, training is closer to 9 months, it would be longer for someone trained on a whole other kind of cockpit and systems layout. Longer if they're expected to fly combat missions in an IADS environment, to the extent it's practical at all.

"The only transferable skills are combat tactics and the basics of aviating" – And even the combat skills may be of questionable usefulness if the planes have markedly different characteristics regarding power, maneuverability, (structural) limits, control authority, agility, range, energy management, etc.

"Flying" is the easy part. I've heard pilots say "If I can get it started, I can fly it".
It is running all the subsystems. Comms, radar, weapons selection. Muscle memory to do that without looking.
But I would also posit that it is not just the pilots. Maintenance is a major factor. Keeping a small fleet of new unfamiliar aircraft fully combat ready is no easy task. You need craploads of tools, equipment, and training.
If you were to drop a dozen Su-27s at Hill AFB (F-35) or Langley AFB (F-22), they'd also have initial problems. We'd figure it out, but some of the tools and parts are totally incompatible.

Agree competely! I would add that as aircraft systems become more and more automated the problem is only getting worse.

As to the "just flying the jet" piece of the puzzle, the  more different types of aircraft a pilot has experience flying, (and the greater the variety),  the less time it takes to become proficient in a new and different aircraft.


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What are the reasons for the particular range of VHF and UHF frequencies?
Generally, VHF frequency range is 30~300MHz and UHF is 300~3,000MHz. (according to Wikipedia). However, in ATC, VHF frequency range is 117.975-137MHz and UHF is 225MHz-400MHz.
Why is there a difference? And what are the reasons for these differences?

It's not clear what you mean by "grounds".  Do you mean why those particular frequencies, why the military wants its traffic on a separate band than civilian, or what?

It is unclear if you ask "why do definition varies between physicists and technical operations?" or something else.

Short answer
The reason for a difference in ranges is historical. The figures from Wikipedia are the recommended ones (by ITU, the reference in radio spectrum matters), however the abbreviations VHF/UHF are also used in related contexts, often in an attempt to discriminate similar uses when being short of other means. In the current case, FAA likely wanted to give different names to different ranges:
118-137.0 MHz: VHF Air/Ground Communications
225-328.6 MHz: UHF Air/Ground Communications

This kind of approximation has actually no practical consequences, except adding confusion to a so much misunderstood field.
Classification of waves according to their frequency is just to determine ranges where waves behave similarly, e.g HF are known to be well reflected by ionosphere, while VHF are less sensitive to such reflection and propagate more along direct light of sight. However this is a progressive and slow change, crossing the border between HF and VHF is like crossing the equator: It has no particular effect (though for the latter, there are lots of good 'proofs' I'm wrong)
There are many examples of radio concepts used approximately, e.g. when we're talking about the 'FM band' to refer to the frequency range used to broadcast using 'wideband FM' (WBFM) modulation required to transmit the large bandwidth of a high quality stereo signal; this range has no particular properties and is not a 'band' and is indeed not technically more appropriate for using WBFM, except regulation forbid other uses.

Close frequencies behaves identically
While there are significant changes between 50 and 600MHz, there is none between 100MHz and 130, 220MHz and 300, or 320MHz and 340.
The only exceptions are not relevant to aviation. Sudden changes in behavior of waves with close frequencies are possible due to absorption of narrow isolated ranges by atmospheric components, e.g. water molecules are small antennas absorbing signals at their resonance frequencies, but resonance occurs at 22 GHz.
Significant differences in radio waves relate to frequencies which are remote
The most significant change in propagation is how much waves can be reflected by the atmosphere and the ground. When such reflections are possible, the communication range is spectacularly increased, as waves can be guided like in an optical fiber towards the receiver area. But again there is no big difference between frequencies belonging to adjacent classes, but near their common border. Broad modes of propagation:

Below 3MHz (a wavelength of 100m), transmission takes advantage of the ground wave (ground currents) to travel on long distances.

Between 3Mhz (100m) and 100MHz (3m), long distance links use the sky wave (reflection on ionosphere, during specific periods of time and according to solar activity, for more on that, see What is the night effect?). Current propagation predictions with close frequencies tending to propagate identically (thanks and credits: Paul L. Herrman et al $\tiny 73$):

Above 100MHz (3m), transmission strictly requires a line of sight and no obstacle in the 1st Fresnel ellipsoid which volume is dependent on the distance between stations, else significant losses occur.

These three first classes are perhaps the most fundamental, then additional divisions have been created above 100MHz (which at the time was already in the "very" high frequency class), because materials can behave significantly differently, e.g. at 150MHz, the only acceptable type of transmission line is coaxial, non-coaxial lines have too much losses, at 15GHz metallic lines are not usable anymore, due to skin effect, dielectric behavior, thermal noise, to name only the first reasons, hollow waveguides are used.
Why are there different classifications for radio waves?
Different segmentations of the whole electromagnetic spectrum have been proposed by different organizations, to focus on the differences that are important for them. These classifications have not to be particularly strict for the reasons explained above, and the limits in publications have varied.
The one Wikipedia is referring to uses segment frequency limits in "3" (3, 30, 300), these limits when expressed in wave lengths become 10m (30MHz), 1m (300MHz), 10 cm (3GHz), etc ($\small \lambda = c / f$).

Source
These limits are the ones recommended by the ITU in ITU-R  V.431, and they are the most commonly used. Not that there are bands without names (but all bands have a specific number).
Sometimes it is useful, or necessary to subdivide the spectrum into smaller chunks. For example TV broadcasting has operated different ranges of frequency spanning HF/VHF/UHF, transmitting at high power. However in the beginning it was not possible to build reliable powerful amplifiers at economical price, except at lower frequencies, so TV started in HF/VHF. As technology improved and higher frequency ranges became workable for amplifiers, new names were used to refer to frequency and associated electronics, exactly like cellular infrastructures and phones are known as 3G, 4G, 5G. We have all seen those names, when tuning the channels: Band I (broadly the "FM broadcast" band), II, III (174-230MHz), IV, V (582-960MHz).
Space communication engineers have their own classification of the SHF and upper bands as letters (L, S, C, Ku, Ka...). This split is well suited to describe the communication capabilities.

For example the US Orbiter communicated with a built-in S band antenna (2GHz), but could deploy a Ku band antenna (16GHz) from the payload bay when in orbit, to increase the transmission rate, e.g. for video streaming.

Radar people have also invented their own bands, for their specific use of the radio spectrum:

Source
And for many persons, waves are also known as short waves and long waves, categories which have been seen during years on radio receivers:

FM/SW/MW/LW on a legacy Grundig Satellit receiver
Likewise many engineers also use the term 'decametric' ('deca') to refer to MF/HF, or 'centimetric' and 'millimetric' for waves in the hyperfrequency domain. Those names have also been recognized by the ITU, though the mapping is somehow approximate.
Indeed aviation has had a need to create frequency segments.
VHF/UHF in aviation
"Aviation bands" include:
 - 108 - 112  MHz NAVAID (VOR, ILS Localizer)
 - 112 - 118  MHz NAVAID (VOR, LASS and SCAT-I))
 - 118 - 137   MHz VHF Air/Ground Communications
 - 62 -  174   MHz Fixed, mobile Communications

 - 225.0 - 328.6 MHz UHF Air/Ground Communications
 - 328.6 - 335.4 MHz NAVAID (ILS Glide Slope)
 - 335.4 - 399.9 MHz UHF Air/Ground Communications
 - 406.0 - 406.1 MHz Satellite Emergency Position Indicating Radio Bcn

Source: FAA order 6050.32 (page 29).
FAA has chosen to see the 225.0 - 328.6 MHz segment as being UHF, even if it starts before 300 MHz. This has no technical impact or implication, wave at 225MHz behave like these at 300, the actual difference from a technology standpoint is more between 150 and 350MHz.
Frequency allocation
In the US, the radio spectrum is allocated to users and final use according to this map (year 2016):

Source
In Europe, spectrum allocation is under ECC responsibility. Current status can be found in "ERC Report 25", aka the European Common Allocation (ECA) Table.


text:
What contra-rotating propellers would be appropriate for this engine?
I am currently getting an X4 cylinder, 150cc, 4 stroke engine 3D CAD Modelled, this engine is initially being designed for Powered Paragliding (PPG), classified as experimental Aircraft, so no certification is required!
I have read several discussions here, that largely relate to large ridged winged Aeroplanes travelling at high ground speed.
PPG is a Low & Slow (22~75kph) Aviation sport, there are obvious differences with this project being;
Most PPG engines max. rev are from 7'000~12'000rpm.
Then a Re-drive is used to slow Prop down to approx. .88~.90 mach.
With a PPG, it is the Wing that sets the Speed in flight, not the engine!
A larger more powerful engine only provides a higher climb rate or maintain lever flight easier.
Most engines of similar capacity swing a 125cm (49/28") Prop at around 2'700rpm to under 3'000rpm.
The engine we are designing uses a unique engine that has replaced the 100yr old conventional crankshaft with a patented Contra-rotating Trilobe centre drive shaft (CDS) technology, that uses two trilobe cams, that strokes each Piston 6 times on One revolution, thus providing 3 combustions in two revolutions of CDS, this engine will not be revving over 3'500rpm maximum.
Engine is currently 12.5kg and 41cm width x 37cm high x 20cm deep.
I am planing on using Two 100cm (40") Contra-Rotating propellers!

I would appreciate it if anyone could assist/help me if this is an appropriate Sized Prop & what Pitch would be best ?

"With a PPG, it is the Wing that sets the Speed in flight, not the engine!" This is true of all aircraft.

@Steve Not exactly. In a conventional aircraft, once you select a certain power setting and adjust stab/elevator trim until you are in level flight, the resulting speed is dependent on the power setting. In a PPG, there is no stabilizer, so level flight will always be at a fixed speed.

@Sanchises In a conventional aircraft, in straight and level flight, if the power setting is increased (and only this is changed), the aircraft will initially speed up, but then it will start climbing. It should stabilize back at the original speed, which is set by the trim.

Why do you think you need contra rotating propellors for an engine predicted to produce only 20hp?

@Steve True. I suppose the quote from the OP is a bit ambiguous, but I think he's hinting at the fundamental lack of horizontal trim rather than basic flight dynamics.

A contra-rotating prop is not needed, it is about making PPG flight a lot Safer, as it will eliminate Torque twist ...caused by one prop!as this engine
As this engine does not have a normal crankshaft we can do this, unlike any other engine.

@Sanchises/@Steve, with a PPG, the Sink rate increases usually caused by  Paraglider speks/design, so an under powered engine will obviously need to rev higher & work harder to maintain level flight, Clime rate is very important if pilots want to climb out of a valley easier.
As yet we are unsure of the HP, Torque will be high enough to compensate.

Anyone with knowledge ...to assist me if 100cm Prop advice ?

Question: conventional 4-stroke radials have an odd number of pots, with your 4 cylinders and 6 strokes per revolution, won't you have the piston-gap problem?  Or is that the point of the tri-lobe cams?

A  Radial has a crankshaft & con rod and one revolution strokes a piston twice.
This engine does 3 full strokes (6), that is equal to 1 1/2 Combustions per 360 degree rotation, when you see our crankshaft it will make more sense.

Click here to see How the Trilobes work
This is image of the Trilobes & Piston Plates

Are you opposed to using a tri-prop? this would be difficult for a 2-bladed propellor.

No, I am not opposed to a three bladed propeller, in fact I understand that as both types are balanced during manufacturing, it will not make any difference in using either one.

In PPG applications, the saying goes, 3 blades are for show, as Usually a two blade are for Go, as a Timber prop usually provides better thrust as there is less flex.
I was thinking of using both, I am of the understanding the last propeller needs a higher pitch to clear the disturbed air of the first prop.

@TheRaptor I'm thinking size restrictions for this large motor. 2 prop will need much more cross-section than a 3 prop

Are you planning on releasing the design.

The Engine is still in CAD design phase, then FEA testing, and finally the release hopefully will happen before the end of this year.
You can see more information on the Raptor-150 Project here:

Contra-rotating props correctly address the problem of how torque
complicates the steering of a PPG.
(To solve this, others have even powered PPGs with large "quadcopters"
where two of the four props are counter-rotating,
despite the screaming of four small fast props.)
In conventional aviation two contra-rotating props typically have the
same diameter and pitch and speed.  For a PPG, keeping them the same size
is particularly useful to cancel torques.
To replace one prop with two, and otherwise keep everything the same,
we should not change the pitch speed or RPM, only the diameter,
to spread the thrust load evenly across both props.
The OP says that a similar engine powers a 49x28" prop at 2700 rpm.
The OP's engine redlines not much past that, so call the RPMs the same.
Then the prop pitch also remains the same, so prop diameter is the only thing left to vary.
Coaxial contra-rotating props are roughly 10% more efficient,
compared to non-coaxial props as on a conventional twin-engine airplane.
So each one of the pair has 45% of the load of the original single prop.
So each prop provides 45% of the thrust of the nominal 49x28" prop.
If all else is equal, thrust varies with the fourth power of diameter.
So we should scale the diameter of the 49x28" prop by 0.451/4 = 0.82.
So the engine should use a pair of 40x28" props.
Exactly the diameter that was guessed.


text:
What are the ground and flight requirements for high performance endorsement?
I'm told ground is proficiency based but that in the plane you have to fly up to 25,000 feet! I don't know anything short of a turboprop capable of doing that, let alone have the ability to rent it. I'm finding different answers everywhere I look! Can anyone cite the FAR on this?

You seem to be confusing a high-performance endorsement with a high-altitude one. Both are in 14 CFR 61.31. They're too long to quote here in full, but the high-performance one comes down to this:

(i) Received and logged ground and flight training from an authorized
  instructor in a high-performance airplane, or in a flight simulator or
  flight training device that is representative of a high-performance
  airplane, and has been found proficient in the operation and systems
  of the airplane; and

The high-altitude one is where your 25,000' number comes from:

(g) Additional training required for operating pressurized aircraft
  capable of operating at high altitudes. (1) Except as provided in
  paragraph (g)(3) of this section, no person may act as pilot in
  command of a pressurized aircraft (an aircraft that has a service
  ceiling or maximum operating altitude, whichever is lower, above
  25,000 feet MSL), unless that person has received and logged ground
  training from an authorized instructor and obtained an endorsement in
  the person's logbook or training record from an authorized instructor
  who certifies the person has satisfactorily accomplished the ground
  training. The ground training must include at least the following
  subjects: [...]

As well as the ground training, you have to do (at least) the following in an aircraft or approved simulator:

(i) Normal cruise flight operations while operating above 25,000 feet
  MSL;
(ii) Proper emergency procedures for simulated rapid decompression
  without actually depressurizing the aircraft; and
(iii) Emergency descent procedures.

There is not a whole lot of difference between flying a 160 hp Skyhawk or Cherokee and a 200+ hp “high performance” Skylane or Cherokee 6. About the only thing I can think of is that you need more right rudder on takeoff. They are usually heavier airplanes so ground control is a little different as well.
I suspect the high-performance endorsement is a holdover from the days when students learned to fly in 65 hp Aeronca Champions since the definition of high-performance from 61.31 is:
(

f) Additional training required for operating high-performance
  airplanes. (1) Except as provided in paragraph (f)(2) of this section,
  no person may act as pilot in command of a high-performance airplane
  (an airplane with an engine of more than 200 horsepower), unless the
  person has—

Most airplanes with more than 200 hp also have a prop control as well as a throttle. So for most people, the biggest thing you need to learn is how to manage the manifold pressure (MP) on the engine with the throttle and the prop speed (RPM) with the prop control.
If you haven’t used a constant-speed prop before, it might take an hour of ground instruction and an hour of flying. If you already know how to use a constant speed prop and how to read the flight manual pages regarding various MP and RPM settings then it might take 10 minutes on the ground and 3 takeoffs and landings.

The FAA used to define a high performance aircraft as having more than 200 horsepower or having retractable gear, flaps, and a controllable propeller. In Aug 1997 they they created the complex endorsement (retractable gear, flaps, controllable propeller) and redefined high performance as simply more than 200 horsepower.


text:
How much of an airline's costs are labor costs?
What percentage of a commercial airline's costs are labor costs? Can an airline run a low-cost operation without reducing the wages for crew and pilots, or subjecting them to long shifts? E.g. Southwest has a history of paying good wages; also personnel is unionized there.
Are there other ways that an airline can reduce costs? Simplified fleets, aircraft utilization, good revenue management, come to mind.

Welcome to aviation.SE! When you say "incidence", do you mean what percentage of a commercial airline's costs are labor?

Yes, in terms of balance sheets.

I edited your question to make it a bit clearer, I hope it's still accurate but you can always reverse or edit again if necessary. Someone may be able to answer clearly about the % of costs that are labor, but the other part about general cost-cutting seems to me very broad and difficult to answer. It also isn't obvious what "good" wages or long" shifts are (pilot working hours are regulated by law in any case), so it could be difficult to come to a definite answer.

It's a bit hard to know how to measure this in some ways. If the airline employs, say, the baggage handlers, ramp workers, and cabin cleaners directly, then surely their wages should count as part of labor costs. But if the airline contracts with a ground handling company for these same services, do they not count as labor costs? And what if the airline happens to own the ground handling company, but it's a separate business?


text:
Can hours at an FAA flightschool be credited to an EASA PPL?
Does anyone know if it's possible to put FAA flight school hours towards an EASA (UK/CAA) PPL?
I've heard answers from "NO" to "Of course" and everything in between, but am struggling to find any documentation that gives a definitive answer one way or another.
From what I can see FAA hours can't be used for credit towards specific training but they can be credited towards the 45 hours total time needed for the license. If anyone has links to appropriate documentation I'd really appreciate it.

Assuming that "flight school hours" means flight time then CAP 804 suggests yes:

3.6 Logging of Flight Hours gained in the USA   Some flight hour recording practices allowable in the USA do not comply with European
  and UK requirements. In particular:

2 pilots flying together in a single pilot aircraft both claiming P1    hours;
One pilot accompanying another on newsgathering or traffic    control flights and claiming P1/PIC when they have not acted as Captain or signed for the aircraft.

Flying hours of this nature cannot be credited towards the
  requirements for Part-FCL or UK Licences.

The last sentence implies that if hours logged in the US do comply with "European and UK requirements" then they can be credited towards licenses. If you need something more detailed and explicit then it may be easiest to ask the CAA directly.

Thanks for the info, CAP804 looks promising. I've already asked the CAA but their responses are useless. First person I talked to said they didn't know, but probably it is possible. Second said they didn't know and probably it is not possible! I'll try them again and see if I have better luck.

@os1 Did you ever find out? If so, might you be willing to post a self-answer with what you found out, for the benefit of others?


text:
Why did the early versions of the Me-109 use a braced stabilizer?
The Messerschmitt Bf-109 had struts holding the stabilizer in place up and including the E version. I marked it with a red circle in the picture below of the 109 E-3 of the Flying Heritage Collection.

Bf-109 E-3 in flight (picture source)
Given that Willy Messerschmitt was fanatical about reducing drag, and contemporaries like the Hawker Hurricane, the Supermarine Spitfire, the Curtiss P-40, the Heinkel 112 or the Dewoitine 520 had cantilevered stabilizers, why would he tolerate a strut on the tail of his new fighter aircraft?

The same on Nord 2002 (source).

Related on PPRuNe. Apparently the struts were removed later, when the tail was redesigned and the horizontal stabilizer was made more aerodynamic (it looks like there was a negative dihedral at the beginning).

To understand that particular design decision, some background may be necessary.
In the 1920s, Willy Messerschmitt had started a small aircraft factory in Bamberg with limited economical success. When he requested financial help from the Bavarian state, he was forced to merge with another aircraft factory in Augsburg, into Bayerische Flugzeugwerke. Since few of his designs enjoyed commercial success, he was forced to accept the production of other designs under license to keep the workforce of the combined companies occupied.
The only Messerschmitt design which had been accepted by Lufthansa was the M.20, and a close friend of a Lufthansa director was killed in a test flight of the M.20. When that director was promoted to the German air ministry and became responsible for selecting aircraft for building up the new Luftwaffe, he made it clear to Messerschmitt that he would avoid purchasing his designs because he disapproved of his reaction to that fatal accident of the M.20.

Messerschmitt M.20 (picture source)
The most successful type of Messerschmitt's designs was the M.23, a two seater sports plane. It had suffered two accidents in which the tailplane broke off in flight, so struts for the tailplane were added while initially produced aircraft had an unbraced tail.

Early Messerschmitt M.23a with ABC Scorpion engine (picture source)
Messerschmitt had gained a reputation for aerodynamically clean and very lightweight designs, and accidents of the M.20 and M.23 in which the tail section failed made pilots wary of the structural soundness of his designs. Nevertheless, his aircraft achieved surprising performance with very limited engine power, so he was unofficially asked to contribute a design when a competition for a new standard fighter was announced in 1934. As an outsider, he had to make sure that his design would be accepted by his critics, so he played it safe and braced the tail, as he had done on the M.37 (which was to become the Bf-108 and was in many ways the dress rehearsal to the Bf-109).
That is the real reason for the struts: Messerschmitt had to play it safe to not threaten his chances as an outsider for a very lucrative contract.

But shouldn't that be on top, because the tail produces a download for stability reasons? I can't imagine that a WWII-era fighter would have a lifting tail, it would get so tiring fighting it without fly-by-wire.

@ptgflyer: Yes, but there is little structure to attach it to. In a taildragger the vertical cannot be mounted very low, it has to be on the upper half of the fuselage. Now you get more fuselage structure below, and attaching the strut to the vertical means beefing this up. Many early tails were braced on both sides, so there was always one loaded in tension.

Hmm, never thought about the ground clearance. Still, wouldn't it be better to mount the other end on the vertical stabilizer?

@ptgflyer: Look at the struts of the M-20: They are more for stabilizing the vertical than for bracing the horizontal. With a propeller in front, you will have asymmetric loads, and those need to be carried into the fuselage. So it is better to use lower struts which can directly lead the torque into the fuselage tube, the only thing which provides torsional stiffness. Relying on upper struts only would need a much stronger and heavier vertical.

Oh, I didn't know that it was for the vertical stabilizer.

The design was carried over from the Bf 108. This would've enabled a lighter structure. The ME-109 versions 'B' through 'E' had them, which was finally removed from the 'F' version. It came back in the 'H' version, which was cancelled.
When the struts were removed in 'F' version, it was found that high-frequency oscillation in the tailplane spar was overlapped by harmonic vibrations from the engine, resulting in failure; this required stiffening of the structure.
To be fair, the Hurricane prototype had struts too.

Source: network54.com

Then the question becomes: Why did both the Bf-108 and the Bf-109 have those struts? The RWD-9, the direct competitor to the 108, had a cantilevered tail even though the wing had struts.

What about the fact that the struts are on the bottom? Shouldn't they be on top to counter the download from the tail? It looks too thing to provide much compressive strength; wouldn't it buckle?


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How is the speed of a helicopter controlled?
How is the speed of a helicopter controlled? Does the pitch of the blade vary for speed while rotor blade moves at a constant speed as with turboprops? Or is there a throttle mechanism for varying the rotational speed of the rotor for forward airspeed?

You may want to remove your final question as it is not related to the main question. Keep your questions focused on a single topic at a time.

I was referring to the fuel usage question, but that was already removed by kevin. The question whether there is a throttle mechanism is completely fine (and is answered in my edited response: there is a manual throttle or an automatic governor)

A helicopter in principle has a constant speed rotor. In fact, the allowed RPM range is very narrow, somewhere between 90-110% nominal RPM. This RPM range is achieved either by a manual throttle or a governor. The blade pitch is directly controlled by the collective.
If a helicopter rotor were perpendicular to the forward speed, you would indeed need to keep increasing the blade pitch (with the collective). However, in a helicopter, the rotor is nearly aligned to the airflow. The vertical 'chunk' of air the rotor takes therefore does not increase that much with increasing speed. At the same time, due to the forward speed the helicopter gains translational lift, which would actually decrease the blade pitch required.

It should be noted however that while in aircraft pilot sets power and desired rpm and the governor sets corresponding blade pitch, in helicopters pilot always sets the blade pitch directly and then either pilot or governor adjusts engine power to keep the rpm within the desired range. So it is constant-speed, but the method of control is very different.

There are many fine articles existing that discuss how the throttle is used to input power into the rotor disc system to lift the helicopter, and how the rotor disc system is tilted to change the direction the helicopter flies. Putting more tilt into the forward direction makes the helicopter fly faster in that direction.
Optimum cruise speed is discussed in this paper, where knots of airspeed vs fuel needed is derived/plotted.  I wouldn't consider fuel wasted if one wanted to go faster, any more than driving 75 mph vs 55 mph on the highway is wasting fuel.  You just get to your destination faster. "Time is Money", yes? So what is worth more - an extra gallon or two of fuel/hour, maybe outrunning a storm in the process, or climbing above turbulent air, vs your time being spent travelling and doing productive work (or vacationing) at your destination?
http://www.eaa1000.av.org/technicl/perfspds/perfspds.htm


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What is the minimum number of engines required for taxiing an airliner?
What is the minimum number of engines required for taxiing for jet airlines from a fuel savings perspective, for 4 engine configurations and 2 engine configurations?
Is using fewer engines counter productive, given that if fewer engines are used more throttle would be required and hence more fuel?
Finally can jumbos like the boeing 747-800 and the airbus A380 taxi with just one engine?

It is extremely common for multi-engine jets to shut off one or more engines while taxiing to save fuel. The A380/747-8 may even be required to do it on narrow taxiways to avoid sucking in FOD since the outer engines can hang over the grass.

Related, maybe duplicate: Taxiing with one engine: Is engine #1 always used or do they switch?

This question states there are some airliners for which the answer is one.


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Are turboprops less safe then jets?
On a recent trip to an airport, I noticed a large number of Bombardier Dash 8s. I wanted to know - are turboprops less safe than traditional jets like the 737 or A320? For instance, I would imagine they are less forgiving with bird strikes.

How do you quantify "less safe"? They may have a higher accident rate just because they are used quite a bit more for small regional flights. I don't think they are any less safe in a bird strike incident, maybe moreso because the bird can't really travel through the engine...

To expand on @RonBeyer's point, take off & landing are the most dangerous part of the flight. Props are used on short-haul flights, so they spend more of their lives in the "most dangerous" part of the flight regime. Therefore, they might show up more often in accident statistics. However, it's far more dangerous to drive to the airport than it is to actually fly to the destination airport, so in that sense, no.

A turbo-prop is a jet engine with an added transmission box = more moving parts and more to go wrong. That issue alone inherently increases mechanical malfunctions.

I don't think this can be answered. Turbo prop aircraft are used in entirely different roles that increase risk. More freight, skydiving, short haul - this skews the statistics.

There is no hard answer to this and it should always be looked at carefully as its dangerous to compare these things. The factors vary widely and a clear cut comparison is generally hard. Twin Turbo-Props may have a lower celling than your average regional jet, they often fly shorter routes and see more cycles compared to their total hourly lifetime, some turbo-props are even in reach of private pilots which puts them in a different operational situation all together but will be lumped in on the statistics.
The most comprehensive study I can find on the topic, and one I feel breaks it down nicely, is this one from NASA

Differences in Characteristics of Aviation Accidents during 1993-2012
  Based on Aircraft Type

Im going to refrain from quoting to much directly as its all relevant and a fairly short 20 page read. The table that seems to sum it up best is the following (refer to study for table explanation):

A bit of a tangent but related, here is a nice article from AOPA comparing the data for Small Jets VS Turbo Props operated under part 91

This chart is not necessarily applicable. For example turbo prop aircraft are more likely to be used for skydiving while jets are not. These and other types of risky operation (insurance stats) that jets may not be being used for skew statistics.

@jwzumwalt I understand that skydiving carries a risk for those jumping out of the plane, but why would it make the flight any less safe?

Ask any sky diving pilot how the flight is flown... max power for 10min, then a wing over diving for the ground and runway. Do it all over again 6 times a day in a poorly maintained aircraft. The most dangerous part of any flight is landing and takeoff and they do it all day every 15min. Turbo props are also more apt to be used for ground spotting, forest fires, pipeline inspection, etc - quit literally the most dangerous types of flying and much more risky.


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Can air to air refueling can be done in the rocket engines as done in the Aircraft jet engines?
Can air to air refuelling can be done with rocket engines as is done with conventional aircraft jet engines? If no then what are the possible hazards or conditions preventing this?

It depends if you are asking about rocket ships or rocket planes. On any note, its unlikely in the lower atmosphere, but in orbit, quite possibly.
There are a few issues you may encounter,

Some rockets use solid fuel which cant be pumped from one tank to the next so you would not be able to refuel on the go.
As @TomMcW mentions in the comments most rocket engines also carry oxidizer which you would need to pass over as well, doubling the volume you normally need to pass
Most rockets use liquid oxygen which is stored at very high pressures, you would need to not only have another craft carrying a specialized tank but a way to transfer the oxygen in the proper state.
You would need to transfer the fuel with out causing a pressure issue that lead to cavitation in the engine. During the design of the Saturn V Engines pressure variances in fuel flow caused serious cavitation issues and even lead to the loss of a test bed engine. While this problem was inevitably solved, the solution (as far as I know) does not account for pumping into the tank during operation.
Rockets move fairly fast and also roll on takeoff so some sort of connection mechanism would need be quite complex. Matching speeds is less of an issue than having something revolve around another object that is rotating on an axis.
Most rocket planes operate above the celling of practical refueling aircraft.

Frankly there is little practical reason as most rocket planes don't really need to refuel. Historically rocket planes like the Bell X-1 or the X-15 were built as test beds to push speed and altitude limits they carried the fuel they needed, burned it, broke the record, and glided home using histories oldest engine, gravity.
Refueling spacecraft has not proved to be a need yet as we have been able to successfully escape earth orbit on a single tank of gas. Building a rocket in space and sending it off has been theorized but there no examples of that yet and in that case you could ferry fuel up in small loads and deal with the docking in orbit.
Once in orbit docking two craft is fairly straight forward, then just connect the fuel lines and pump (presumably with out the engines running)...

The rolling makes connecting easier, not harder. Because the article says they can roll, and do roll to align, but not that they would roll continuously. That means they can roll to align the fuel receptacle with the boom and then maintain that roll.

@JanHudec I dont think it can roll selectively like that (to intercept another track), it needs to be rolled in order to maintain trajectory. I think a roll to meet another course would cause issue on the launch path but I need to do some more reading on on exactly how it works.

the article is pretty clear that they roll to intercept the track; they then maintain the orientation to maintain it. And (in symmetrical rockets) it is not really needed, but rather a simplification for the engineers so they don't have to include rotation of the coordinates everywhere.

For a rocket launch, a significant problem that hasn't been mentioned is fuel flow rate.  The Saturn V's first stage carried  203,400 gal of kerosene & 318,000 gal LOX ((770,000/1.2 million liters) of liquid oxygen, which it burned in under 3 minutes (by which it was well on its way to orbit).  Imagine trying to match speed, connect hoses, and transfer that much fuel in that short a time.

Refueling is done a few times per year on the ISS. A visiting spacecraft arrives, docks and transfers some of its fuel to tanks on the ISS for its engines.
Refueling while in orbit is relatively simple: docking is a solved problem, and there is no turbulence etc. to make things difficult.
Refueling while a rocket engine is running is more difficult. You could consider the Shuttle an example: its main engines are fed from the external tank, so fuel has to be transferred from the tank to the orbiter. This is doable because the tank is already attached before liftoff.
Flying two rockets in close formation in flight (while still in the atmosphere) and transferring fuel between them is very difficult - the shockwaves coming off each rocket will interfere with the other one, I'd expect there to be lots of turbulence making it difficult for two rockets to fly in close formation and reliably hook up for the fuel transfer.

Both aircraft (tanker & tankee) need to be really close, and their relative velocity needs to be zero. Both could be achieved by rockets, as the wing loading is very high, and thus the interference by air movement/density changes is really low.
The problem is the third requirement: You need to be able to pass a hose between the two. Rockets typically are supersonic, and i see no way of doing that at those speeds.
Also: Rockets are 90% fuel at launch, so the action of giving / receiving fuel will alter their mass relatively more than the refuelling of a plane.
If your question was just about rocket- driven planes: Those usually have no fine regulation of their rocket drives, instead  using surfaces for control, so i doubt those would be able to pace themselves beside a tanker.

An additional consideration is that you’d have to pass along oxidizer as well as fuel

... or shovel bricks of solid fuel :-)

Another factor to consider: the extreme speed and altitude of anything rocket propelled.
Rockets, which carry both fuel and oxidizer, tend to operate well in excess of Mach 1, typically at altitudes in excess of 100,000 feet. Any lower, and they could use air and dispense with carrying oxidizer.
True that the ISS is refueled and reprovisioned regularly, but it is a very stable platform with a high level of mass that orbits in microgravity, as does a resupply vessel.
Lower down, the rocket is still fighting off gravity, where even a minor problem can result in a rapid change of direction. Getting two ships linked up at Mach 4 would be extremely risky... just one little deviation, and it's kaboom for both of them... wouldn't be enough time to react.
And, there is the expense involved versus the benefits. If you're thinking of a hyper speed transport going halfway around the world at Mach 5 or 6 at over 150,000 feet, the tanker needs not only the fuel and oxidizer to match the transport's speed, but the fuel to transfer as well, plus enough fuel to account for the extra weight of the transfer fuel and oxidizer. It would be a hideously expensive proposition.
The same holds true for a launch to orbit ship. A refueling rocket would need to be quite a bit larger than the launch rocket, and two rocket launches would have to be coordinated, so why not just dispense with the idea of refueling and make the launch vehicle larger?

In addition to the comments above, note that it takes several minutes of skilled aviating to rendezvous an aerial tanker with the vehicle to be refueled. Since the initial boost phase of a typical launch is only of order ~minutes long, by the time the rendezvous is accomplished, it's time to jettison the first stage...

I don't think "pilotage" means what you think it means.

to me it refers to the activity or process of guiding an aircraft to a goal using navigation and control inputs.

" using fixed points of reference on the sea or on land, usually with reference to a nautical chart, aeronautical chart or topographic map, to obtain a fix of the position of the vessel, aircraft or land traveler with respect to a desired course or location. "

edited.   hope this helps.


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stall with max power
I saw a video of a test flight of a GA plane and it stalled with max power and with a moderate AOA (angle of attack). How can a plane stall with max power (with the wings flying below the critical angle of attack)?

I'm not entirely sure what you saw or what you're asking, but this question might help. You can't determine AoA by just looking at the aircraft, so it might have been at a moderate pitch angle, but a high AoA.

Can you link to the video so we can see what is going on?

"A wing can stall at any speed" is a useful mantra; don't assume you're within the flight envelope because you're fast.

Being on the back-side of the power curve is a real thing. Practice a power-on stall and you'll realize just how much "power" you need to stay flying when you are slow/high AoA.

If you are wondering how an airplane can stall in straight and level flight with the engine running at full power, the answer has to do with the power curve.
However, by definition it cannot stall "with the wings flying below the critical angle of attack stall". The only reason it might appear to do so while in a straight and level flight would be due to heavy icing or some other factor that reduces the critical angle of attack.

A plane (airfoil) can stall at any airspeed and/or power setting so long as the critical angle of attack is exceeded. Airplanes stalling only below a specified airspeed is a common misconception largely due to the fact planes are usually listed with a “stall speed” below which the aircraft will generally stall in most situations. However if the critical angle of attack is exceeded at a higher speed a stall can also occur. The only way to know the critical angle of attack is from an angle of attack measurement device installed on the airframe it is inherently somewhat different than the aircrafts attitude.

You know what would make stalls impossible? Rockets. Underneath the body. Gone into a stall? No problem, engage space-rockets.

If it stalled, by definition, it did exceed the critical angle of attack.  Most GA aircraft have a critical AOA between 12-18°.  Pretty shallow compared with aircraft equipped with LE and TE high lift devices.

You're probably referring to a power-on stall. This type of stall is the result of climbing more steeply than the engine can provide power for.
From AOPA

Pilots can become distracted or disoriented after takeoff and climb too steeply. The airplane slows, the wing angle of attack increases, and an unintentional stall (and potential spin) is the result.


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Is it allowed to exit the runway by opposites High Speed Taxiway?
Is it allowed to exit the runway on a High Speed Taxiway to the opposite side? (see red line in image below). Assume the situation allows it, like airplane limits, airport congestion, weather, etc.

Yes.  One of the airlines I flew for prohibited the use of high speeds.  We had to slow on the runway and exit at a standard or reverse unless they were unavailable.  It was part of the opspecs, not just an informal rule.

It's not really a regulation question, at least not in the way you think. There's 2 possibilities:

A controlled airfield: in an airfield which has air traffic control all movements require a clearance, if the tower clears an airplane to use a taxiway then that is all that airplane is allowed to do unless there's an emergency of some kind. It would be unusual for ATC to direct an airplane to use a taxiway which has such a tight turn, but there's no reason they wouldn't if it the situation called for it
An uncontrolled airfield: in this situation there's nobody in a tower telling pilots what to do, all movements are at pilots' discretion. Pilots can use any taxiway in any way they please as long as it doesn't put them in potential conflict with another airplane

yes this is allowed, and common at certain airports
If you land in such a manner to come to a reasonable taxi/turn speed where the closest available exit taxiway is a "opposite high speed" taxiway, At this point you can either taxi forward to the next available 90 or high speed, -OR- use the closest "opposite high speed"
Tower and other landing traffic will usually perfer that you exit via the nearest taxiway


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Do hot air balloon pilots file flight plans?
Are hot-air balloon pilots ever required to file flight plans? (can they file?)

A quick look at the FAA rules regulating hot air balloons makes it sound like, in the USA, they can enter any sort of airspace provided they can do it safely.  So, theoretically, they could file a flight plan or at least alert local ATC to their activities.
All of that being said, having been involved in hot air balloon operations before, I think it would not be terribly feasible.
Firstly, flying a hot air balloon outside of Visual Flight Rule conditions (being able to see several miles) would be extremely dangerous, so you wouldn't need to file a flight plan for that.
Secondly, you generally only want to fly a hot air balloon in very sparsely populated areas (Class G airspace), and while you could have a flight plan there really isn't a need.  A more congested area (Class B or Class A) would be extremely dangerous to navigate in a hot air balloon.  It's pretty hard to get out of the way, since controlling where you are going is...iffy sometimes.
So, in summary, yes it could be done, but in the vast majority of cases there's little need to do it.  Other than to just alert local ATC that you will be in the area.

It's also often suggested that fixed-wing pilots file VFR flight plans for search-and-rescue reasons; does that apply or no?

@raptortech97 Not really, in a hot air balloon you need to have a chase vehicle following you around (which pulls the trailer you pack the ballon in so you can stow it when you land, wherever you happen to land...).  They'll be keeping an eye on you, so there's really no need for what you propose.

As a balloon pilot: no we do not.  We do fly regularly in classes G, D, and E and will occasionally wander into class C; but it is very frowned upon...and you better have an aircraft radio or at least call the tower to let them know you are there.   Of course balloons always have right-of-way so if you see us get out of the way; we can't control where we're going.

Is your comment about right-of-way facetious, or factual? Is there a regulation specifying your immediate right-of-way, or do you mean "because you cannot control your directionality with any serious degree of control, everyone else should look out."

@CGCampbell It's factual in the U.S. per 14 CFR §91.113(d)(1): "A balloon has the right-of-way over any other category of aircraft."

@dvnrrs  Thank's....that may have taken a few moments to dig up.  I find this interesting that it is well known to balloonists that we have right-of-way but we often have to explain that to ATC or to other aircraft pilots.  Specifically I've had to warn-off several ultralight pilots several times about flying too close to us.

@RamaFan Interesting... my impression is that the right-of-way rules are quite common knowledge among pilots. Not to single anyone out but I don't know the above commenter's qualifications; they may not be licensed. (Lots of enthusiasts-only on ASE.) It's certainly required knowledge for the PPL for all categories, and very likely to come up in the oral exam / written test. No idea about ATC.

@dvnrrs  It's probably something fixed wing guys know very well for other fixed wing aircraft and helicopters but many just don't encounter balloons often enough to remember.  On the converse side I don't remember very much on the right-of-way for who lands at the airport...we had to know it for the test but I've never had to use it being only a Balloon Pilot.

I am not a licensed pilot, simply an aviation enthusiast. That is why many of my questions are basic. I was not under the impression that a PPL/CPL is required to attend to this exchange. :) (I know it's not, I am just saying it to reinforce it.)

@RamaFan Also consider that ultra light pilots don't actually need licenses to operate...  There's no test for them, knowledge of the rules is just a useful suggestion... They may actually be completely unaware.

@RamaFan Could you specify which country/countries your answer applies to? Rules do vary from state to state.

ICAO Standards do not differentiate between hot air balloons and other flights when it comes to flight plans. The following is from Rules of the Air (Annex 2):

3.3.1.2
  A flight plan shall be submitted prior to operating:
  a) any flight or portion thereof to be provided with air traffic control service;
  b) any IFR flight within advisory airspace;
  c) any flight within or into designated areas, or along designated routes, when so required by the appropriate ATS authority to facilitate the provision of flight information, alerting and search and rescue services;
  d) any flight within or into designated areas, or along designated routes, when so required by the appropriate ATS authority to facilitate coordination with appropriate military units or with air traffic services units in adjacent States in order to avoid the possible need for interception for the purpose of identification;
  e) any flight across international borders.
Note.— The term “flight plan” is used to mean variously, full information on all items comprised in the flight plan description, covering the whole route of a flight, or limited information required when the purpose is to obtain a clearance for a minor portion of a flight such as to cross an airway, to take off from, or to land at a controlled aerodrome.

As mentioned in the note, a flight plan may simply be an abbreviated flight plan, which is submitted over the radio. Such a flight plan would typically just include identification, type, flight rules, persons on board and intentions.